Diversity, Activity, and Abundance of Sulfate-Reducing Bacteria in Saline and Hypersaline Soda Lakes

Abstract

Soda lakes are naturally occurring highly alkaline and saline environments. Although the sulfur cycle is one of the most active element cycles in these lakes, little is known about the sulfate-reducing bacteria (SRB). In this study we investigated the diversity, activity, and abundance of SRB in sediment samples and enrichment cultures from a range of (hyper)saline soda lakes of the Kulunda Steppe in southeastern Siberia in Russia. For this purpose, a polyphasic approach was used, including denaturing gradient gel electrophoresis of dsr gene fragments, sulfate reduction rate measurements, serial dilutions, and quantitative real-time PCR (qPCR). Comparative sequence analysis revealed the presence of several novel clusters of SRB, mostly affiliated with members of the order Desulfovibrionales and family Desulfobacteraceae. We detected sulfate reducers and observed substantial sulfate reducing rates (between 12 and 423 mol/dm 3 day ؊1 ) for most lakes, even at a salinity of 475 g/liter. Enrichments were obtained at salt saturating conditions (4 M Na ؉ ), using H 2 or volatile fatty acids as electron donors, and an extremely halophilic SRB, strain ASO3-1, was isolated. Furthermore, a high dsr gene copy number of 10 8 cells per ml was detected in a hypersaline lake by qPCR. Our results indicate the presence of diverse and active SRB communities in these extreme ecosystems.Soda lakes are extreme environments with pH values up to 11 and salt concentrations up to saturation. These high pH values are maintained due to the high buffering capacity of sodium carbonate/bicarbonate, which are among the major anions in solution. The salinity can vary from 5 to 30 g/liter for hyposaline lakes to up to 500 g/liter for hypersaline lakes. Despite these extreme conditions, soda lakes are highly productive and harbor diverse microbial communities (6,11,25,35) responsible for the element cycling.The sulfur cycle, driven by haloalkaliphilic sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB), is one of the most active element cycles in soda lakes. SOB are represented by members of the class Gammaproteobacteria belonging to the genera Ectothiorodospira, Thioalkalivibrio, Thioalkalimicrobium, and Thioalkalispira. Bacteria belonging to the first genus are phototrophic sulfur purple bacteria, while the other three genera are obligate chemolithoautotrophs (30), utilizing various reduced inorganic sulfur compounds as electron donors. Members of the Ectothiorodospira and Thioalkalivibrio genera are particularly remarkable in their potential to grow in saturated alkaline brines.Although more than 100 SOB strains have been isolated from soda lakes (30), so far only four species of SRB, i.e., Desulfonatronovibrio hydrogenovorans (37), Desulfonatronum lacustre (22), Desulfonatronum thiodismutans (23), and Desulfonatronum cooperativum (38) have been isolated, and they are all low-salt-tolerant alkaliphiles. However, although Desulfonatronovibrio hydrogenovorans is a low-salt organism, it was isolated from Lake Magadi, a hypersalin...

Bacterial diversity and activity along a salinity gradient in soda lakes of the Kulunda Steppe (Altai, Russia)

“…The rates were comparable with previous measurements (Foti et al 2007) and, in general, corresponded to characteristic values of eutrophic marine sediments (Lein et al 2002). Salinity seems to have no effect on the sulfate reduction process in the studied soda lakes.…”

“…In the last decade, special attention has been given to the investigation of the microbial communities in soda lakes using both traditional isolation methods (Duckworth et al 1996;Sorokin et al 2004;Sorokin and Kuenen 2005b) and molecular biology techniques (Humayoun et al 2003;Rees et al 2004;Scholten et al 2005;Foti et al 2007). Few reviews (Zavarzin et al 1999;Jones et al 1998) summarize these results, showing that soda lakes contain representatives of the major trophic and phylogenetic groups of prokaryotes, and that they can be considered as autonomous systems, in which cycling of nutrients is close to complete.…”

Influence of salts and pH on growth and activity of a novel facultatively alkaliphilic, extremely salt-tolerant, obligately chemolithoautotrophic sufur-oxidizing Gammaproteobacterium Thioalkalibacter halophilus gen. nov., sp. nov. from South-Western Siberian soda lakes

“…The culture medium was inoculated with a mixture of sediments from hypersaline soda lakes in South-Western Siberia (Altai, Russia). The description of the sediments is given elsewhere (Foti et al 2007). Development of the culture was followed by the monitoring of thiosulfate consumption.…”

Planktonic bacterial community composition of an extremely shallow soda pond during a phytoplankton bloom revealed by cultivation and molecular cloning

“…Recently, the cultivation dependent and independent analyses of planktonic and sediment microbial communities include, among others, studying the soda lakes of South-East Siberia, Russia (Foti et al 2007(Foti et al , 2008, North-East Mongolia (Sorokin et al 2004), Inner Mongolia, China (Zhang et al 2001;Ma et al 2004a), Lonar Lake, India (Wani et al 2006;Joshi et al 2008), the East African Rift Valley, Kenya and Tanzania (Rees et al 2004;Mwirichia et al 2010Mwirichia et al , 2011, Wadi An Natrun, Egypt (Mesbah et al 2007), as well as Mono Lake, California, USA (Hollibaugh et al 2001;Humayoun et al 2003) and Soap Lake, Washington, USA (Dimitru et al 2008).…”

“…Sequences related to thiosulfate-reducing species of Dethiosulfatibacter aminovorans and Fusibacter paucivorans as well as the sulfate-reducing species Desulfobotulus sapovorans and Desulfonatronum lacustre were also found among the Böddi-szék clones. In previous studies, the presence of sulfate-reducing phylotypes was reported mainly from the sediment of saline and soda lakes (Foti et al 2007(Foti et al , 2008Mesbah et al 2007). …”